DStruct

  # configure attribute types
  class MyStruct < DStruct::DStruct
    attributes strings: [:string], integers: [:int], booleans: [:bool], arrays: [:arr]
  end
  
  # define dry-validation schema - http://dry-rb.org/gems/dry-validation/
  MyValidationSchema = Dry::Validation.Schema do
    key(:string).required(:str?)
    key(:int).required(:int?)
    key(:bool).required(:bool?)
    key(:arr).required(:array?)
  end
  
  # initialize without casting
  struct = MyStruct.new({string: '123', int: 123, bool: true, arr: [1], date: Date.today})
  struct.add_validation_schema MyValidationSchema
  puts struct.to_h   # => {string: '123', int: 123, bool: true, arr: [1], #<Date: 2016-03-22 ...>}
  puts struct.valid? # => true
  puts struct.errors # => {}
  
  # initialize with casting
  struct = MyStruct.new({string: 123, int: '123', bool: 'true', arr: 1, date: '2016-03-22'})
  struct.add_validation_schema MyValidationSchema
  puts struct.to_h   # => {string: '123', int: 123, bool: true, arr: [1], #<Date: 2016-03-22 ...>}
  puts struct.valid? # => true
  puts struct.errors # => {}
  
  # unknown key
  struct = MyStruct.new({unknown_key: '123'})
  struct.add_validation_schema MyValidationSchema
  puts struct.valid? # => false
  puts struct.errors # => {unknown_key: 'unknown key'}
  
  # missing keys
  struct = MyStruct.new({})
  struct.add_validation_schema MyValidationSchema
  puts struct.valid? # => false
  puts struct.errors # => {:string=>["is missing"], :int=>["is missing"], :bool=>["is missing"], :arr=>["is missing"]}
  
  # invalid values
  struct = MyStruct.new({string: nil, int: nil, bool: nil, arr: nil})
  struct.add_validation_schema MyValidationSchema
  puts struct.valid? # => false
  puts struct.errors # => {:string=>["must be filled"], :int=>["must be filled"], :bool=>["must be filled"], :arr=>["must be filled"]}
  
  # multiple schemas
  Schema1 = Dry::Validation.Schema{key(:string).required(:str?)}
  Schema2 = Dry::Validation.Schema{key(:int).required(:int?)}
  struct = MyStruct.new({string: '123', int: 123})
  struct.add_validation_schema Schema1, Schema2
  puts struct.valid? # => true

gem 'd_struct'